This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-259351, filed Aug. 29, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a sheet separation unit and an image forming apparatus equipped with the sheet separation unit.
2. Description of the Related Art
Image forming apparatuses such as facsimiles, printers or copy machines incorporate a sheet separation unit configured to separate, for example, stacked recording cut-sheets of paper from one another and to convey them to an image forming mechanism. Many sheet separation units employ a friction separating method.
The sheet separation unit for separating, from one another, sheets of paper stacked in a cassette and conveying them comprises: a unit main body including pivot bearings; a separation/conveyance roller rotatably provided in the unit main body to draw sheets of paper stacked in a cassette and convey them; a separation member located parallel to the separation/conveyance roller, including pivots that project from the each end of the separation member in the direction of their axes and are received in the pivot bearings of the unit main body, the separation member being swingable on the pivots to and away from the separation/conveyance roller, the separation member separating paper sheets drawn by the separation/conveyance roller when it is in contact with the roller; and a separation spring provided in the unit main body and applying a force to the separation member to enable the separation member to be brought into pressure contact with the separation/conveyance roller.
In accordance with the rotation of the separation/conveyance roller corresponding to the direction of sheet conveyance, a few of recording cut-sheets stacked in the cassette are drawn, beginning from the uppermost, to a contact portion of the separation/conveyance roller and the separation member. The thus drawn recording paper sheets are separated from one another by the friction of the rotating separation/conveyance roller and the separation member, and conveyed one by one.
In the sheet separation unit, when each recording paper sheet passes between the separation/conveyance roller and the separation member, the separation member slightly swings on the pivots away from the separation/conveyance roller. After each recording paper sheet has passed, the separation member pressed by the separation spring slightly swings on the pivots to the separation/conveyance roller. As a result, the separation member collides with the outer peripheral surface of the separation/conveyance roller. Thus, in the sheet separation unit, each time recording paper sheets are separated from one another, vibration and collision occur and hence an unpleasant noise occurs.
To enable the sheet separation unit using the friction separating method to separate paper sheets with the occurrence of noise suppressed, several countermeasures have been taken to date. Jpn. Pat. Appln. KOKAI Publications Nos. 7-133033 and 9-249321 disclose sheet separation units devised to suppress such noise. In these units, as well as the separation spring configured to bring the separation member into pressure contact with the separation/conveyance roller, elastic members are employed to apply their elastic forces to the separation member in the radial direction of the pivots. In this structure, vibration of the separation member during the sheet separation and hence occurrence of noise are suppressed by pressing the pivots of the separation member against the respective inner peripheral surfaces of the pivot bearings.
In the above sheet separation units using the friction separating method, however, the friction, which is caused by the elastic members between the pivots and their bearings when the pivots are pressed against the bearings, interrupts the swing operation of the separation member, i.e. interrupts the operation of bringing the separation member into contact with the separation/conveyance roller to separate recording paper sheets.
In other words, when swinging the separation member on the pivots to the separation/conveyance roller, using the force of the separation spring, the friction caused between the pivots and the bearings acts as a resistance that reduces the pressure (separation pressure) applied to the separation member to put it into pressure contact with the outer peripheral surface of the roller. As a result, smooth separation and conveyance of paper sheets cannot be executed.
On the other hand, if the force of the elastic members used to press the pivots of the separation member against the bearings of the unit main body is reduced, it is difficult to effectively suppress the vibration of the separation member and hence the occurrence of noise during the sheet separation.
Therefore, there is a need for a sheet separation unit capable of suppressing the noise of a separation member incorporated therein when it separates paper sheets, while maintaining a smooth separation of the sheets.
A sheet separation unit comprises: a separation/conveyance roller; a separation member to be brought into contact with the roller so as to separate paper sheets drawn by the roller; an elastic member configured to bring the separation member into pressure contact with the roller; and a pair of elastic holding members that apply axial forces to respective opposite end sections of the separation member from the outside. The axial forces pressurize the opposite end section toward a central portion of the separation member, and the elastic holding members pressure hold the separation member in a state in which the separation member can swing to and away from the roller.